Safety circuit in electrically operated devices

ABSTRACT

The invention discloses a safety circuit for electrically operated devices, which turns on the device in question, based on its position and design, only if handling and posture by the operator is completely correct and proper and the circuit, moreover, is static and insensitive to outside influences due to the use of sensor switches.

FIELD OF THE INVENTION

The present invention relates to a safety circuit in electricallyoperated devices, more particularly, to such a device having severalinteracting switch elements to enable current to flow to operate thedevice. These circuits are used with electrically operated devices toeliminate the risk of injury to the user in the event that the devicesare handled improperly.

Such circuits generally provide that an operating current or at least acontrol current is directly switched. The switches themselves areusually mechanical in structure. However, it has been found that suchknown safety circuits have serious drawbacks and disadvantages aspointed out below.

One disadvantage is that activation requires only that one or moreswitches be depressed. If the user so desires, this is often done inpractice, he can operate at least one switch by simply attachinginsulating tape to maintain that switch in a depressed or activatedstate.

If larger safety devices are involved, in practice, an additional"bridge" is quite often installed by the users. If magnetic switches areinvolved, these are often rendered inoperative by add-on permanentmagnets.

The voltages used in these devices often lie in a range that isdangerous to humans.

The mechanisms of such mechanical switches, and thus their function, aresusceptible to external forces, such as atmospheric humidity, corrosionand fouling by dirt, dust or other small debris.

Because of their size, it is not always possible to position theswitches optimally on the device.

According to U.S. Pat. No. 3,651,391, the embodiment in FIGS. 1 and 2has a first sensor switch as an on-off switch, and a second sensorswitch maintains the flow of current. This second switch is used solelyas a safety switch.

The disadvantages of this prior art structure are rapidly apparent.

If the first switch (on-off switch) is turned on, the device can beactivated unintentionally by accidentally touching the second sensorswitch. There then exists a risk of injury to the user. To reduce thisrisk, at least one monitor must be provided in connection with the firstone-off switch. Thus, this structure does not provide the safetyobjective according to the present invention and is, moreover,expensive.

In a second embodiment (FIGS. 5 and 6) of U.S. Pat. No. 3,651,391, twohands (body parts) are required to operate the device, one hand acutatesonly a first sensor switch and the other hand only a second sensorswitch. In this embodiment, only the presence of the respective hand,but not its posture or position, is critical. It is not possible torequire both the presence of a hand and a particular position of thishand with only one sensor switch per body part. This structure istherefore also not usable in a device that can be held and oeprated withonly one hand.

This kind of contemplated safety is often circumvented by the user byshort-circuiting one of the switches in order to increase the speed ofthe operating sequence.

According to the present invention, circumventing safety in this way isnot possible. The present invention requires that the posture of eachbody to be predetermined.

According to a third embodiment (FIGS. 7, 8 and 9) of U.S. Pat. No.3,651,391, two sensor switches are provided, both of which must beactivated to produce a flow of current. One of the switches is providedto turn the device on and off. The second switch keeps the currentflowing as long as it is touched. With this structure also, a situationcan arise where the device is activated with the first swtich turned onby accidentally touching the second switch. Also, the posture of thebody part here is by no means critical.

DE-PS (German Patent) 37 16 623 C1, discloses a tilt switch which allowsa current to flow only if the switch reaches a certain angle ofinclination. Such a tilt switch is utilized only as an auxiliaryelement, according to the present invention, which can replace one ofthe two contact elements as disclosed.

Contact elements (sensor switches) are basically known from DE 27 53 314C2. In this patent specification, the function of a sensor switch isexplained. According to the present invention, such a sensor swtich is,if necessary, improved to the extent of being able to operate in moistspaces. This is achieved by introducing a galvanic separation into theswitch electronics. In DE 27 53 314 C2, no indication of the use of sucha switch for safety circuits, such as those underlying the invention, isdisclosed.

According to DE 26 27 663 C2, the metal foils are provided as switchelements, which work as follows: The metal foil lying on the outside ofthe device is touched by a person and consequently changes its mass,i.e., increases it. This changes the capacitance of the actuatingelement, which consists of the whole of the two metal foils together. Inthis way, the switching process is triggered. The second metal foil inthis case lies inside and is not touched by the person. Also, thispatent specification is not concerned with solving safety problems thatare associated with the operation of a device.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a safety circuit, bywhich an electrically operated device receives an operating current onlyif a predetermined, safe operating state is guaranteed, and to producethis state.

This object is thus in contrast with the usual prior art requirements,even according to the safety requirement of U.S. Pat. No. 3,651,391,wherein the flow of current that is present is interrupted if the devicecan no longer be handled safely.

The present invention provides for a predetermination of what is to beconsidered safe and thus proper handling. Safety is determined by thetwo measures of "position" and/or "posture" of the device and/or of thebody part that is to operate the device, and the circuit is madedependent on these measures above and beyond the normal usual switchingmeasures.

Position is defined as the position, the site, the location of thedevice.

Posture is defined as the attitude/position of the operating body part,usually the hand, with respect to the device.

It is thus apparent that the main advantage of the present invention isthat the device receives current only if it is in a necessarilyprescribed safe state (position) and/or if the hand (body part)operating the device is in the correct posture for this purpose.

The object of the present invention, is achieved by combining thefollowing conditions or characteristics:

1. High safety for the operator and the surrounding environemnt, withrespect to:

a) When is the device turned on, when is it turned off?

b) What voltage is used?

2. It must not be easy to manipulate or by-pass the switch (bridging,gluing, etc.).

3. The switch must be insensitive to outside influences or forces asmuch as possible.

4. The switch must be easy to manufacture and produce and usable indevices.

The basic idea of the invention is thus not to merely turn off adevice--as has usually been done in the past in the case of amalfunction, i.e., a danger,--but to ensure that the device is turned ononly if it is completely properly operated and thus to counteract allpossible malfunctions and danger points.

This is achieved according to the invention by ensuring that the safetyswitch can be activated, not as has usually been done in the past, byonly one condition (a push button is depressed) being met; but rather,several conditions must be met simultaneously and/or in sequence.

According to the invention, this means that in an embodiment such as inFIGS. 5 and 6 of U.S. Pat. No. 3,651,391 two sensor switches would haveto be provided for each body aprt, i.e., a total of four for the device.

According to the first condition, contact with human skin i.e. theperson operating or using the device, or iwth the ground potentialcorresponds to depressing the prior known mechanical safety switch.

As the second condition, position is introduced as an additional safetyfactor. The posture of the body part (hand) of the person in contactwith the device and/or the position of the device itself.

For example, the positions of at least two contact elements, mustrespectively be placed so that they can be reached by the body part onlyif a person's hand assumes a predetermined posture on the device and, ifnecessary, also exerts a predetermined pressure. This can be determinedin advance by the sensitivity of the contact plate of the sensor switchand the control electronics.

In addition, the control voltage should be completely harmless. This isachieved according to the present invention by using the groundpotential as a control pulse, and the circuit thus works with no sourceof electric current.

The sensor switch can be neither bridged electrically nor mechanicallyfixed.

The sensor safety circuit is insensitive as much as possible to outsideinfluences, since the control electronics can be encapsulated inplastic, and the simple contact surfaces offer very little opportunityfor outside effects or forces and also contain no moving mechanisms.

Production is readily possible, since this is a new combination of knownparts, in a specific arrangement, with a new object and an unobviousresult. In terms of installation, this new sensor safety circuit allowsthe manufacturer of such a device more options than in the case, of theeprevious mechanical safety switches.

BRIEF DESCRIPTION OF THE DRAWING

Other objects and advantages of the present invention will be apparentupon reference to the accompanying description when taken in conjunctionwith the following drawings, which are exemplary, wherein:

FIG. 1 is a perspective view of a hand drill incorporating the presentinvention and held by the user;

FIG. 2 is a side elevational view of an electric thread cutter;

FIG. 3 is a perspective view of an iron;

FIG. 4 is a schematic view of the wiring diagram for the hand drillaccording to FIG. 1;

FIG. 5 a schematic view of the wiring diagram for the thread cutteraccording to FIG. 2;

FIG. 6 is a schematic view of the wiring diagram for the iron accordingto FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As may be seen in FIG. 1, a hand drill incorporating the presentinvention is indicated generally at 10 and is of the type which has ahand or pistol grip 2. The pistol grip extends downwardly from one endof a body, portion 8 and the other end has a chuck 9 from which extendsa bit or drill 9a as known in the art. The hand grip 2 is provided withcontact plates 3 and 4 so disposed as to be contacted by the hand 5 of aperson using the hand grip as shown in FIG. 1. The contact plates 3 areinsulated from each other and from the hand drill 10 and are recessed inthe handle 5 of the hand drill in such a manner that both contacts 3 and4 are touched or contacted only when the person correctly holds the handdrill 10 in one hand, or if so desired in both hands.

An electronic control circuit 6A which may be encapsulated in plastic,is mounted within the body 8 of the hand drill and is connected toelectric leads a to a electric drive motor M. The electrical leads aalso extend from the other side of the control circuit downwardlythrough the handle 2 and outwardly at the bottom thereof to a source ofelectrical energy. The control circuit 6A thus controls the flow ofelectrical operating current to the drive motor M.

Thus, the band 5 of the user, as shown in FIG. 1 brings a groundpotential 11, which is specific to this particular person to the contactplates 3 and 4. The electronic control device 6A then transmits theoperating current through the leads a for the drill only if the groundpotentials d are both present from both contacts 3 and 4. The electricalcircuit utilized for this purpose is shown in FIG. 4 wherein 1 indicatesthe sensor safety switch. It is also within the scope of this inventionto utilize the current produced by the two ground potentials b forswitching since the intensity of the ground potential d increases as theuser more tightly grips the handle and thus the electrical contacts 3and 4.

If hand 5 (or hands) must leave the specified posture or have too loosea grip, the device immediately turns off.

In FIG. 2, there is indicated generally at 20 an electric thread cutterwhich incorporates the present invention. The thread cutter 20 is showncutting threads on an end of a pipe 21 which is secured in a vice 22 ina known manner. The electric thread cutter 20 is provided with anelongated hand grip 23 upon which is mounted a single contact 3 which isgripped by the hand 5 of the operator when using the thread cutter. Thethread cutter is further provided with a position or tilt switch 7 whichswitches another control signal c to the controlled electronic unit 6Bas shown in FIG. 5. Thus, when the ground potential d generated by thehand of the user and position switch c transmits a control signal c tothe electronic unit 6B this electronic unit will then permit the flow ofelectrical current through leads a to the motor 7 in a manner asdescribed above.

This electric thread cutter 20 should not be tilted beyond a certainpredetermined angle. Contact element (3) is recessed in the handle 23and insulated from the thread cutter in such a way that a person touchescontact 3 only when using it properly. Ground potential (b) that isspecific to it is thus brought to the contact plate which sends it on tocontrol electronics 6B.

The switch (7), whose switching state is dependent on its position,vertical or horizontal, sends a pulse (c) to control electronics (6)when the electric thread cutter is in the correct position. If bothpulses are present, control electronics 6B puts operating current (a)through to the motor M.

According to FIG. 3 an electric iron 30 is provided, which has a contactplate (3) built in, insulated from the device, such that a persontouches it with his hand (5) when properly using the iron. The groundpotential that is specific to the person is thus transferred to contactplate (3). The plate sends the potential to control electronics 6C shownin FIG. 6.

Position switch (7), whose switching state is dependent on its position,vertical or horizontal, directs a pulse (c) to control electronics 6Conly if the iron is in the upright position as shown. The latter putsthrough operating current (a) only if at least one of two pulses (b orc) is present. This means: the iron is held in the hand or is set downcorrectly in the upright position.

In this embodiment of FIG. 3, the basic concetp of the invention: "toturn on, if operated properly" is clearly demonstrated. All possiblemalfunctions are thus excluded. The only thing is that this is thespecial case where proper operation does not have to be limitedabsolutely to a certain time and date, but can take place at differenttimes and in different ways.

In the embodiment according to FIG. 3, the person's hand (5), shown,brings earth potential (b) that is specific to it to contact plate (3).The latter controls the control electronics 6C. Position switch (7)switches another control signal (c) to control electronics 6C when theiron is set down properly, in the upright position. Control electronics6C transmits operating current (a) to the hot plate of the iron when atleast one control pulse (c or b) is present.

It is to be noted that in FIG. 6, the electronic unit 6C is providedwith an OR which controls a control signal from either a sensor 3 or theposition switch 7. In FIG. 5, the electronic unit 6B is provided with anAND circuit which requires both control signals from both the sensor orcontact 3 and position swtich 7 in the thread cutter 20 of FIG. 2. InFIG. 4, the electronic unit 6A is also provided with an AND circuit fortransmitting both control signals from both contacts 3 and 4.

It is thus apparent that the circuit of the invention has the followingfeatures:

a) A very high degree of safety. The device turns on only when carefullyand correctly operated and turns off immediately in case of danger.

b) There is no potential on the contact plates.

c) The contact plates cannot be bridged or fixed as switches.

d) The circuit is fail-safe, since it cannot be influenced from theoutside.

e) The circuit is not subject to wear.

f) The circuit can be constructed not to spark.

g) The circuit is static. No mechanism is necessary forthe actuation ofthe switches.

h) The contact plates are positioned flush with the surface, forexample, a handle of the device.

i) Good handling is possible.

The invention thus incorporates the following advances over the priorart:

a) In general, it was necessary to avoid having electrically operateddevices that are turned off at the instant of danger; rather, it ispreferable for these devices to be turned on only when they are usedabsolutely safely and correctly, thus eliminating all possible risks.

b) Subsequently, it was necessary to introduce the posture of theperson's body part wtih respect to the device, the hand that operatesthe device, and/or the position of the device itself as decisive safetyfactors.

c) Finally, the following steps were also necessary:

I. Mechanical devices are replaced by the static sensor switch.

II. No current is put through; rather the ground potential is present.

This invention relates not only to sensor switches that operate with anearth potential. This mode of operation has only one advantageousconfiguration. It goes without saying that also other sensor switches,for example, capacitively operating switches according to the prior art,can also be used. See in this respect DE 26 27 663 C 2.

The circuits shown in FIG. 2, 4 and 6 also operate just as well withother sensors on the devices connected to them, for example, capacitiveoperating sensors.

We claim:
 1. Safety circuit in hand operated electrical devices having ahand grip for a hand of the user, comprising a plurality of interactingswitch elements to enable electric current to flow from an externalsource to an electric drive motor in said device, at least two of saidswitch elements are disposed on the hand grip that triggers a functionof the switch elements; said switch elements comprising electronicallyoperating contact elements insulated from one another and from thedevice, said contact elements being so positioned on the hand grip thatthe contact elements are simultaneously touched by the user's hand onlywhen said user's hand is in the proper and correct operating posturewith respect to the device to enable the flow of electric current tooperate the device.
 2. Safety circuit in hand operated electricaldevices having a hand grip for a hand of the user comprising a pluralityof interacting switch elements to enable current to flow from anexternal source to an electric drive motor in said device, at least twoof said switch elements are disposed on said device, at least one ofsaid switch elements comprises a contact element insulated from thedevice, and is so disposed on the hand grip that the contact element istouched by the user's hand only when the user's hand is in the properand correct operating position with respect to the device, and the otherswitch element responds to the positioning of the device in its correctoperating position to enable the flow of electric current to operate thedevice when the contact element of said one switch element issimultaneously touched by the user's hand.
 3. Safety circuit of claim 2,wherein the switch elements are placed in an AND-circuit or anOR-circuit.
 4. Safety circuit of claim 1 or 2, wherein the switchelements respond to one another in a time-staggered fashion.
 5. Safetycircuit of claim 1 or 2, wherein the contact elements respond to theearth potential.
 6. Safety circuit of claim 1, wherein connecting thecontact elements of the switch elements to one another electrically butwithout earth potential does not trigger control electronics (6). 7.Safety circuit of claim 1 or 2, wherein the contact elements are matchedto the contact intensity by the user's hand.
 8. Safety circuit of claim1 or 2, wherein the operating voltage is immediately turned off in theevent of mishandling.
 9. Safety circuit of claim 1 or 2, wherein thecontact elements are placed in the area of the handle of a movableoperating device.
 10. Safety circuit of claim 1 or 2, wherein thecontact elements are fixed in place.
 11. Safety circuit of claim 1 or 2,wherein the contact elements end flush with the surface of the hand gripor handle.
 12. Safety circuit of claim 1 or 2, wherein the contactelements are placed in a watertight arrangement in the surface of thehand grip or handle.